A stick-shaped ignition coil includes a coil portion, a control portion, and a tower portion. The coil portion is located in an axially intermediate position of the ignition coil. The control portion is located on the upper end side of the ignition coil. The tower portion is located on the lower end side of the ignition coil. The coil portion is constructed of a cylindrical case that receives a center core, a primary coil, and a secondary coil. The control portion is constructed of a box-shaped case that receives an igniter. The cylindrical case and the box-shaped case are individually formed. Subsequently, the cylindrical case and the box-shaped case are connected to each other.
As shown in FIG. 10, a conventional ignition coil, which is disclosed in JP-A-2000-277362, includes an elongated cylindrical coil case 120 and a circuit case 125 that are integrally connected to each other. The coil case 120 receives a center core, primary and secondary coils (none shown). The circuit case 125 has a connecter 126, and receives an electric circuit (not shown). The coil case 120 and the circuit case 125 are individually formed. Subsequently, the upper outer circumferential periphery of the coil case 120 is press-inserted into a hole portion formed in the bottom portion of the circuit case 125 via multiple protrusions 121. The protrusions 121 are formed on the outer circumferential periphery of the coil case 120, and the protrusions 121 are pressed and deformed when the coil case 120 is press-inserted into the circuit case 125.
The outer diameter of a coil portion of an ignition coil needs to be reduced in recent years. Therefore, a coil case, which receives a center core, primary and secondary coils, is reduced in wall thickness in a conventional ignition coil disclosed in JP-A-2003-51416. In this structure, the coil case having thin wall thickness cannot be stably connected to the circuit case due to insufficient rigidity of the coil case. Therefore, the upper end portion of the coil case is press-inserted into the hole portion of the circuit case, and subsequently, the press-insertion portion between the coil case and the hole portion needs to be filled with glue to enhance rigidity. In this structure, the connecting process becomes complicated. Besides, a supporting portion need to be formed on the end portion of the primary spool to support a lead portion of a primary winding of the primary coil. As a result, the outer diameter of the primary spool becomes large.